1. Field of the Invention
This invention relates to a solder coated lid for a package for housing an electronic device, such as a semiconductor device, and to a package employing such a lid. In particular, it relates to a solder coated lid for a package for housing an electronic device which enables the package to be sealed without damaging electronic devices mounted in the package.
2. Description of the Related Art
In recent years, there has been a strong desire for decreases in the size and thickness of electronic equipment such as portable telephones and portable computers. At the same time, there has also been a great desire for decreases in the manufacturing costs of such electronic equipment.
As electronic equipment becomes smaller and thinner, it becomes easier for electronic components disposed therein, such as IC chips and quartz crystal units, to be adversely affected by heat, vibrations, and deformation at the time of manufacture. Mounting of electronic devices close to one another within electronic equipment tends to increase such problems.
FIG. 1(a) is a schematic cross-sectional elevation of a portion of a conventional package. In this example, a lid 18 is installed on the upper end 16 of a ceramic base 14 housing various electronic devices, such as a quartz crystal unit 12, connected to each other by wire bonding 10. FIG. 1(b) is an enlarged schematic exploded cross-sectional elevation showing the structure of the lid 18 and the upper end 16 of the ceramic base 14 in detail.
As shown in detail in FIG. 1(b), the upper end 16 of the base 14, which is made of an alumina ceramic, for example, is metallized with a tungsten layer 20 by the simultaneous sintering method or other suitable method. A nickel layer 22 is provided atop the tungsten layer 20, and the nickel layer 22 is covered by a silver brazing layer 24. A Kovar ring 26 (which is nickel plated on its surface) is installed atop the nickel layer 22, and then a Ni/Au layer 28 is provided atop the silver brazing layer 24.
The lid 18 comprises a body 19 made of Kovar, and the body 19 is plated to form a nickel film 30 on its surface. The lid 18 is installed on the upper end 16 of the base 14 of the package and is secured atop the Kovar ring 26 by seam welding.
This method of sealing a package involves numerous manufacturing steps, and installing the lid 18 through the ring 26 and performing brazing are difficult. Furthermore, this method has problems with respect to costs. In addition, with this sealing method, it is difficult to achieve reduce the size and thickness of the package. Thus, there is a need for improved methods and structures for sealing a package for electronic devices.